The catalytic domain of the Serine/Threonine Kinase, Glycogen Synthase Kinase 3STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. GSK3 is a mutifunctional kinase involved in many cellular processes including cell division, proliferation, differentiation, adhesion, and apoptosis. In plants, GSK3 plays a role in the response to osmotic stress. In Caenorhabditis elegans, it plays a role in regulating normal oocyte-to-embryo transition and response to oxidative stress. In Chlamydomonas reinhardtii, GSK3 regulates flagellar length and assembly. In mammals, there are two isoforms, GSK3alpha and GSK3beta, which show both distinct and redundant functions. The two isoforms differ mainly in their N-termini. They are both involved in axon formation and in Wnt signaling.They play distinct roles in cardiogenesis, with GSKalpha being essential in cardiomyocyte survival, and GSKbeta regulating heart positioning and left-right symmetry. GSK3beta was first identified as a regulator of glycogen synthesis, but has since been determined to play other roles. It regulates the degradation of beta-catenin and IkB. Beta-catenin is the main effector of Wnt, which is involved in normal haematopoiesis and stem cell function. IkB is a central inhibitor of NF-kB, which is critical in maintaining leukemic cell growth. GSK3beta is enriched in the brain and is involved in regulating neuronal signaling pathways. It is implicated in the pathogenesis of many diseases including Type II diabetes, obesity, mood disorders, Alzheimer's disease, osteoporosis, and some types of cancer, among others. The GSK3 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.